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SubjectRe: [PATCH 0/20] return f_fsid for statfs(2)
On Jan 19, 2009  20:39 -0600, Dave Kleikamp wrote:
> On Tue, 2009-01-20 at 07:36 +0800, Andreas Dilger wrote:
> > The whole point of fsid (for NFS) is that this identifies the filesystem
> > over reboot, even if the block device ID changes, or if the filesystem
> > doesn't have a block device at all (e.g. cluster filesystem).
>
> I guess that just demonstrates how little I know about what the fsid is
> about. Would it be preferable for file systems that have a uuid to use
> that instead? Of course anything is an improvement over zeroes.

Yes, that is what the ext* patches do - fold the 128-bit UUID into a 64-bit
fsid so that it is constant across reboots. The chance of UUID collision
is about 1/2^32 due to birthday paradox, which is fairly low, and in case
this happens one of the filesystem UUIDs can be regenerated.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.



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